Drüsenfarbstoffe aus Labiaten: Strukturen von 16 Diterpenen (Coleone und Royleanone) aus Coleus coerulescensGÜRKE

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Abstract
Leaf‐gland pigments from labiatae: structures of 16 diterpenoids (coleons and royleanones) from Coleus coerulescens GÜRKEThe Abyssinian labiate Coleus coerulescens has been investigated for its leaf‐gland pigments. From the very complex mixture of abietanoic diterpenoids the following pure constituents were isolated and their structures established: Diosphenols: coleon C (1a), 16‐O‐acetyl‐coleon C (1b), coleon W (1f); A/B‐trans‐6, 7‐diketones: coleon D (2b), 16‐O‐acetyl‐coleon D (2c), coleon V (2a); Spiro‐coleons: 7,12‐bis(O‐desacetyl)‐coleon N(3a), 12‐O‐desacetyl‐coleon N (3b), coleon O (4), 6,12‐bis (O‐desacetyl)‐coleon R (5a), 12‐O‐desacetyl‐coleon R (5b), 3‐O‐desacetyl‐3‐O‐formyl‐coleon Y (5g); Royleanones: The abeo‐compounds 6a, 6b, and 7. Main compounds are 3b, 5e and 5g. This is the first record of a co‐occurrence of diosphenols, 6,7‐dioxo‐coleons, spiro‐coleons and royleanones. Preliminary experiments show that solvolytic opening of the cyclopropane‐ring followed by tautomerisation, oxidation to hydroxy‐p‐benzoquinones or elimination to quinomethanes and subsequent nucleophilic attack of the solvent leads to compounds with a 2′‐substituted propyl group at C(13), thus supporting the biosynthesis of the unusual coleon E side chain.

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